Twin mass flywheel

ABSTRACT

A twin mass flywheel comprising two co-axially arranged flywheel masses which are mounted for limited angular rotation in a drive and over-run direction relative to each other, and a plurality of pivotal linkages. Each pivotal linkage comprises a first link pivotally connected to one of the flywheel masses, a second link pivotally connected to the other of the flywheel masses and a pivot pivotally connecting the first and second links. The action of the links controls relative rotation of the flywheel masses, and the controlling action of the links is supplemented by one or more assister springs which operate over a significant proportion of the full drive direction range of relative rotation. The twin mass flywheel may further include end stops to positively limit relative rotation of the flywheel masses in the drive and over-run directions and may additionally include end stop resilient means which cushion the relative rotation of the flywheel masses just prior to contact of the end stops. A common support member may partially support both ends of the end stop resilient means and one end of the assister spring.

FIELD OF THE INVENTION

The present invention relates to a twin mass flywheel for transmittingtorque and absorbing or compensating for torsional vibrations such ascan arise in a vehicle transmission assembly.

SUMMARY OF THE INVENTION

More particularly the invention relates to a link-type twin massflywheel comprising two co-axially arranged flywheel masses which aremounted for limited angular rotation relative to each other; and aplurality of pivotal linkages comprising a first link pivotallyconnected to one of the flywheel masses, a second link pivotallyconnected to the other of the flywheel masses, and a pivot for pivotallyconnecting the first and second links, in which the action of the linkscontrols relative rotation of the flywheel masses.

It is the object of the present invention to provide an improved form oflink-type twin mass flywheel.

Thus according to the present invention there is provided a link-typetwin-mass flywheel in which the controlling action of the links issupplemented by one or more assister springs which operate over asignificant proportion (e.g. the majority) of the full drive directionrange of relative rotation.

In such a link-type twin mass flywheel the circumferentially actingsprings come into operation in at least one of the following conditions:

a) between 0% and 60% of the total relative rotation of the flywheelmasses in the drive direction and in particular between 0% and 50% ofthe total relative rotation of the flywheel masses in the drivedirection. e.g. typically 25%.

b) between 0 degrees and 12 degrees of relative rotation of the flywheelmasses in the drive direction. e.g. typically 7 degrees.

Typically the total possible assister spring compression is greater than10 degrees of relative rotation of the flywheel masses e.g. typically 20degrees of relative rotation of the flywheel masses.

The total assister spring rate may be less than 20 Nm per degree ofrelative rotation of the flywheel masses e.g. typically 12 Nm per degreeof relative rotation of the flywheel masses.

Also for a given engine installation at the maximum deflected relativerotational position of the flywheel masses at a steady engine speed,further significant deflection of the assister springs is stillpossible. This further deflection is used to accommodate relativerotation occurring during transient engine conditions e.g. during enginestart.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall now be described, by way of example only, withreference to the accompanying drawings in which;

FIG. 1 is an axial cut away view of a link-type twin mass flywheelaccording to the present invention taken in the direction B of FIG. 2,

FIG. 2 is a radial composite cross section taken along the line 2--2 ofFIG. 1 without showing shoe 82 for clarity.

FIG. 3 is an equivalent view to FIGS. 1 of a second embodiment of a linktype twin mass flywheel according to the present invention;

FIG. 4 is an enlarged view of part of FIG. 3;

FIG. 5 is a cross section view taken along the line 5--5 of FIG. 3 and

FIG. 6 is a cross section view taken along the line 6--6 of FIG. 3.

FIG. 7 is an embodiment that shows the end stop resilient means as apair of concentric springs acting in parallel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 and 2 there is illustrated a link-type twinmass flywheel 10 which is formed from two flywheel masses 11 and 12.

One flywheel mass 11 (also known as an input flywheel mass) is fixed toa crankshaft (not shown) of an internal combustion engine by way of acentral hub 14 and bolts (not shown) which pass through holes 18. In usea friction clutch (not shown) is secured to the second flywheel mass 12(also known as an output flywheel mass) to connect the second flywheelmass with an associated gearbox (not shown).

Under normal drive and over-run conditions the twin mass flywheel 10rotates in an clockwise direction in the view shown in FIG. 1 asindicated by arrow E.

The flywheel mass 11 comprises the central hub 14, a main housing plate15, a cover plate 13 and a starter ring 27 which is welded to the mainhousing plate 15. An inner bearing retaining plate 28 is fixed to thehub 14 by rivets (not shown) to retain a bearing 19 on which secondflywheel mass 12 is mounted. Housing plate 15 is fixed to central hub 14by screws 16.

The second flywheel mass 12 comprises a flywheel plate 31 with an outerbearing retaining plate 29 and pivot plate 30 both fixed to the flywheelplate 31 by bolts 32.

Pivot plate 30 has an annular inner portion 30A with plurality of lugs30B which form part of pivots 43, a plurality of slotted lugs 30C whichform part of an end stop unit 70, and a plurality of lugs 30E which acton respective spring units 80.

Relative rotation between two flywheel masses 11 and 12 is primarilycontrolled by a plurality of pivotal linkages 40. A plurality ofassister spring units 80, a friction damping device 50 and end stopunits 70 act in parallel with the pivotal linkages 40 to help incontrolling the relative rotation of the two flywheel masses 11 and 12at predetermined specific relative angular positions or overpredetermined specific angular ranges.

Each pivotal linkage 40 comprises a first link 41 pivotally mountedbetween a centre hub portion 33 of the flywheel plate 31 and pivot plate30 by way of a first pivot 43 and a second link 42 (in the form of aparallel pair of arms 42A and 42B pivotally mounted on the flywheel mass11 by way of a second pivot 44. The two links 41 and 42 are pivotallyconnected to each other by means of a third pivot 45. It will be notedfrom FIG. 1 that the first pivot 43 is positioned radially inwardly ofthe second and third pivots 44 and 45. The first link 41 is formed as abob weight mass.

Under no-load conditions with the clutch disengaged, centrifugal forceacts on the pivotal linkages 40 and particularly on the first link 41and urges the linkages in a radially outward direction with pivot 45adopting a position radially outboard of pivot 43 as shown in FIG. 1(this position is regarded as the neutral position between the drive andover-run directions of relative rotation of the flywheel masses i.e. theposition adopted by the linkages then the twin mass flywheel is rotatingand transmitting zero torque). At higher rotational speeds thecentrifugal force is greater and whilst this does not affect theconfiguration under no-load conditions it greatly affects the forcerequired to move the flywheel mass 12 relative to the flywheel mass 11i.e. the flywheel torsional stiffness.

If the clutch is engaged and power is transmitted in the drive directionfrom flywheel mass 11 to flywheel mass 12 there is a tendency for thetwo masses to rotate relative to each other (flywheel mass 11 rotatesclockwise relative to flywheel mass 12 when viewing FIG. 1). Atrelatively low speeds when the influence of centrifugal force is smallerthe flywheel masses move readily relative to each other i.e. theflywheel torsional stiffness is relatively low. However at relativelyhigh speeds the influence of centrifugal force is much greater andrelative rotation of the flywheel masses requires greater torque i.e.the flywheel torsional stiffness is relatively high. Thus the flywheeltorsional stiffness is speed sensitive.

If the clutch is engaged and power is transmitted in the over-rundirection from flywheel mass 12 to flywheel mass 11 the effects aresimilar to the above except that the direction of relative rotation isreversed (flywheel mass 11 rotates anticlockwise relative to flywheelmass 12 when viewing FIG. 1) and in the embodiment shown in FIG. 1 thefirst link 41 folds between the second link 42 ie. between arms 42A and42B.

Thus the controlling influence of the pivotal linkages is operable atany rotational speed of the twin mass flywheel and also any relativerotation position of the flywheel masses.

In accordance with the present invention the assister spring units 80help in controlling the relative rotation of the twin mass flywheel overa limited angular range in the drive direction.

Each assister spring unit 80 is mounted between housing plate 15 andcover plate 13 and consists of an assister spring 81 and a shoe 82. Theassister spring 81 consists of two concentric springs 81A and 81B bothmounted between third abutments in the form of a shoulder 83A of a pin83 at one end of assister spring 81 and the shoe 82 at the other end. Inan alternative embodiment the assister spring 81 could consist of asingle spring or some other type of resilient means e.g. a block ofelastomeric material.

The pin 83 is fixed rotationally fast with the flywheel mass 11. Theaxial sides of the shoe 82 fit into pockets 84 in the housing plate 15and cover plate 13, in such a manner to ensure the shoe is axially andradially fast but circumferentially movable to a limited extent withrespect to flywheel mass 11. When installed one end of the shoe 82 abutsthe end 84A of the pockets 84 and the assister spring 81 is under arelatively small amount of compression.

Each end stop unit 70 consists of a sleeve 71 fixed between housingplate 15 and cover plate 13 by a screw and nut 72 which is positioned inthe slotted lug 30C.

The twin mass flywheel is required to transfer engine torque to theassociated gearbox. The term "engine torque" means the torque which isproduced and is also maintainable by the engine at a particular speed.These engine torques are produced when the engine is running above itsidle speed and act only in the drive direction. Engine torque can varybetween zero (e.g. engine running at idle speed, clutch disengaged) andthe maximum engine torque figure.

Furthermore the twin mass flywheel is also required to transfertransient torques. Such transient torques are produced as a result ofinertia loads and can not be maintained for very long periods.Furthermore transient torques can act in both the drive or over-rundirections and in particular can be higher than the maximum enginetorque figure.

Under conditions of relatively low rotational speed and high enginetorque (necessary in the drive direction) relative rotation betweenflywheel mass 11 and 12 occur until a fourth abutment in the form of lug30E contacts shoe 82 (in this case after 7 degrees of relative rotationfrom the neutral position). Typically such conditions might occur whenan associated vehicle is moving relatively slowly (say 5 kph) with theclutch fully engaged and the engine throttle is suddenly fully openedresulting in the engine speed progressively increasing as the speed ofthe vehicle increases. Under these conditions each assister spring couldinitially be partially compressed by lug 30E moving shoe 82 andsubsequently as the engine speed rises the centrifugal forces acting onthe bob weights progressively return the flywheel masses to near theirneutral position and the assister spring controlling influence ceases aslug 30E disengages shoe 82. It should be noted that it is particularlyadvantageous to have the assister springs operating at relatively lowengine speeds since the cyclic variations in torque produced by anassociated internal combustion engine are more pronounced at low speedsand the assister spring helps to control these cyclic variations intorque as well as controlling the average underlying maintainable enginetorque.

Under extreme transient torque drive conditions relative rotation of theflywheel masses causes the shoe 82 to move in pockets 84 and compressthe spring pack 81 until sleeve 71 contacts one end 73 of slotted lug30C whereupon relative rotation stops (in this case after a total of 26degrees of relative rotation from the neutral position).

Typically such extreme transient drive conditions might occur at verylow rotational speeds and very high torque loads, for example duringengine start or engine stop when the flywheel speed is below normal idlespeed inertia torque loads can be generated which are far in excess ofthe maximum engine torque produceable by the engine.

Under extreme transient torque over-run conditions of very lowrotational speed and very high torque loads in the over-run direction(such as engine start and engine stop), relative rotational betweenflywheel mass 11 and 12 occur until sleeve 71 contacts the other end 74of slotted lug 30C whereupon relative rotation stops (in this case aftera total of 15 degrees of relative rotation from the neutral position).

The end stop units 70 are arranged to prevent the first, second andthird pivots 43, 44, and 45 of any linkage 40 becoming aligned and toensure that the springs 80 are not overstressed.

The operation of the multi-plate friction damping device 50 is not partof the subject matter of this invention. A full description of itsoperation can be found in the Applicant's prior GB patent application 9505750.1. It suffices to say that damping device 50 frictionally dampsthe relative rotation of flywheel masses 11 and 12.

FIGS. 3 to 6 show an alternative embodiment of a twin mass flywheel 110according to the present invention in which components which fulfilsubstantially the same function as components in the twin mass flywheel10 are numbered 100 greater.

The main differences between twin mass flywheel 110 and 10 are asfollows:

a) twin mass flywheel 110 incorporates end stop resilient means 85 whichoperate under extreme conditions of low rotational speed and high torquein the drive or over-run direction of relative rotation of the flywheelmasses;

b) associated assister springs 181 and end stop resilient means 85 arepartially supported by a common support member 90, and

c) the end stop arrangement is modified.

The twin mass flywheel 110 incorporates three end stop resilient means85, each consisting of a resilient means 86 drive shoe 87D and anoverrun shoe 87OR. In the example shown resilient means 86 comprisesthree elastomeric discs 86B bonded to each other in a stack and ametallic spacer 86A bonded to each end of the stack of elastomericdiscs. In further embodiments each end stop resilient means may compriseother forms of elastomeric material, in particular a single block ofelastomeric material or one or more metallic helically wound springse.g. a pair of concentric springs 185 acting in parallel as shown inFIG. 7

Each end stop resilient means 85 is mounted between first abutments offlywheel mass 111 defined by the combination of a tab 101 of cover plate113 and an end stop portion 91D,910R of the common support member 90.

Common support member 90 is made from a strip of steel which issubsequently bent into shape. The cross section profile of the commonsupport member consists of substantially circular drive and overrun endstop portions 91D,91OR joined by a shoe guide portion 92 and also anassister spring abutment 93 joined to over-run end stop portion 91OR andan assister spring guide portion 94 joined to drive end stop portion91D.

The common support member 90 is sandwiched between the cover plate 113and main housing plate 115 with a fixing rivet 95 passing throughaligned holes in the main housing plate 115, and cover plate 113 andeach drive and over-run end stop portion 91. Thus each common supportmember is located by two fixing rivets 95.

Operation of the twin mass flywheel 110 is substantially the same as theoperation of twin mass flywheel 10 with fourth abutment 104 acting tocompress the assister spring under conditions of low engine speed andhigh engine torque.

However when the flywheel masses are approaching the limit of relativerotation in the drive direction under extreme transient torque driveconditions second drive abutments 102D on flywheel mass 112 contactcorresponding drive shoes 87D and cause the resilient means 86 to becompressed. Subsequent further relative rotation causes drive end stopportion 130D of pivot plate 130 to contact drive end stop portion 91D ofthe common support member whereupon relative rotation ceases.

Sufficient relative rotation of the flywheel masses in the overrundirection under extreme transient torque over-run conditions will resultin each second over-run abutment 1020R contacting corresponding over-runshoe 870R and causing the resilient means to compress until relativerotation is halted by over-run end stop portion 130R of pivot plate 130contacting over-run end stop portion 910R of the common support member.

It can be seen from FIG. 4 that starting from the neutral position asthe flywheel masses rotate relative to each other in the drive directionthe assister spring engages after 7 degrees, the end stop resilientmeans engages after 21 degrees and the end stop engages after 26degrees. Correspondingly as the flywheel masses rotate relative to eachother in the over-run direction the end stop resilient means engagesafter 8 degrees and the end stop engages after 13 degrees.

It should be noted that the end stop resilient means therefore operatesover five degrees (26-21) of relative rotation in the drive directionand five degrees (13-8) of relative rotation in the over-run direction.Further embodiments may have the end stop resilient means operating overa different range of rotation of the flywheel masses in the drive andover-run direction.

Note that the total travel of the end stop resilient means in the drivedirection (5 degrees) is approximately 26% (i.e. less than 30%) of thetotal travel of the assister springs (19 degrees).

Contact between the end stops of the twin mass flywheel 10 or 110 causesnoise and can also cause high stress in some components. Thus in thetwin mass flywheel 110 the end stop resilient means act to cushion or insome circumstances eliminate contact between the end stops thus reducingnoise and reducing stress in some components.

During compression of the end stop resilient means 85 the shoe guideportion 92 acts to guide the movement of the drive or over-run shoes87D,870R.

Each spring unit 180 consists of a spring 181 and a shoe 182. Eachspring 181 comprises a pair of concentric springs 181A and 181B bothsupported at each end by third abutments 103 in the form of an assisterspring abutment 93 of the common support member 90 and an assisterspring shoe 182.

In alternative embodiments the assister spring 181 could consist of asingle spring or some other type of resilient means e.g. a block ofresilient material.

The assister spring abutments 93 and shoes 182 fit into pockets 184pressed into the cover plate 113 and housing plate 115. Loads generatedby the assister springs 181 are transferred through the assister springabutments 93 to the main housing plate 115 and cover plate 113 viacontact with the ends of the pockets 184.

Under certain conditions the mid portions of the assister springs 181can bow radially inwards and assister spring guide portions 94 areprovided on the common support member 90 to counteract this tendency.

The common support members thus carry out several functions and can bemade simply and cheaply.

Thus it can be appreciated that the assister springs 80, 180 areprimarily designed to assist control of the flywheel masses underspecific maintainable conditions of engine torque in the drivedirection. This is quite distinct from the operation of the end stopresilient means 85 which are primarily designed to control very hightransient torques produced as a result of inertia loads in both thedrive and over-run directions often with the engine running at sub idlespeeds.

This distinction is borne out by the fact that the combined spring rateof all the assister springs is significantly less than the combinedspring rate of all the end stop resilient means when present. Forexample, a modern 2 liter sedan car producing say a maximum enginetorque of 180 Nm which includes a link type twin mass flywheel of thetype described might have a combined assister spring rate of less than20 Nm per degree of relative rotation of the flywheel masses and if theflywheel included end stop resilient means the combined end stopresilient means spring rate may be in the range 40 Nm to 150 Nm perdegree.

It can be advantageous to arrange the ratio of the combined assisterspring rate to the combined spring rate of the end stop resilient meansto be in the range 1:2 to 1:6.

Using the above example, whilst the vehicle can produce a maximummaintainable engine torque of 180 Nm, under transient conditions such asengine start-up and stop extreme transient torque levels of up to 1000Nm can be achieved momentarily due to inertia loads and it is theseextreme torque loads that are ultimately controlled by the end stops andend stop resilient means.

This contrasts with maintainable relatively low speed high engine torqueconditions when the centrifugal effect on the bob weights is low and therelative,rotation is controlled by a combination of the bob weights andthe assister springs.

Also the end stop resilient means can operate as a result of rapidlyreversing inertia loads. During for example engine start-up the flywheelmasses may move rapidly from the full drive position to the full overrunposition and back to the full drive position several times as the engineaccelerates from stationary to engine idle speed. It can be particularlyadvantageous if the end stop resilient means are made from anelastomeric material. Such elastomeric materials have significantly morehysteresis than say an equivalent helically wound compression spring andthey thus absorb some of the energy of the system when compressed. Thismeans that subsequently when the twin mass flywheels begin to movetowards the other extreme of relative rotation the kinematic energy isless and subsequent contact between end stops is reduced or eliminated.

It should be noted that even though the assister springs operates overthe majority of the relative rotational movement in the drive direction,this does not necessarily mean that the assister springs operate overthe majority of time when the associated engine is in the drivecondition. This is because at mid to high engine speeds the bob weighteffect is sufficient to maintain the twin mass flywheel at or near itsneutral position and at relatively low engine speeds (say idle speed)with the clutch disengaged or an associated gearbox in neutral theengine torque fluctuations are not sufficient to move the twin massflywheel far from its neutral position. Typically a vehicle might spendthe majority of time at mid to high engine speeds or at idle with theclutch disengaged or with the gearbox in neutral.

In further embodiments it is possible to have any number of linkages incombination with any number of assister springs (i.e. not necessarilyone assister spring with each linkage). Furthermore such embodiments mayadditionally have any number of end stop resilient means (i.e. notnecessarily one end stop resilient means with each linkage).

We claim:
 1. A twin mass flywheel comprising two co-axially arrangedflywheel masses which are mounted for limited angular rotation in adrive and over-run direction relative to each other, and a plurality ofpivotal linkages comprising a first link pivotally connected to one ofthe flywheel masses a second link pivotally connected to the other ofthe flywheel masses and a pivot pivotally connecting the first andsecond links, in which the action of the links controls relativerotation of the flywheel masses, and the controlling action of the linksis supplemented by one or more assistor springs which operate over asignificant proportion of the full drive direction range of relativerotation.
 2. A twin mass flywheel as defined in claim 1 in which one ormore assistor springs come into operation between 0% and 60% of thetotal relative rotation of the flywheel masses in the drive direction.3. A twin mass flywheel as defined in claim 1 in which one or moreassister springs come into operation between 0 degrees and 12 degrees ofrelative rotation of the flywheel masses in the drive direction.
 4. Atwin mass flywheel as defined in claim 1 in which total possible springcompression of the assistor springs is greater than 10 degrees ofrelative rotation of the flywheel masses.
 5. A twin mass flywheel asdefined in claim 1 in which the combined spring rate of the assistersprings is less than 20 Nm per degree of relative rotation of theflywheel masses.
 6. A twin mass flywheel as defined in claim 1 in whicheach assistor spring consists of a pair of concentric springs acting inparallel.
 7. A twin mass flywheel as defined in claim 1 which includescorresponding end stops on each flywheel mass to positively limitrelative rotation of the flywheel masses in the drive and over-rundirections and also includes end stop resilient means which cushion therelative rotation of the flywheel masses just prior to contact of thecorresponding end stops.
 8. A twin mass flywheel as defined in claim 7in which each end stop resilient means acts to cushion the relativerotation of the flywheel in both the drive and over-run directions.
 9. Atwin mass flywheel as defined in claim 7 in which the combined springrate of the end stop resilient means is in the range 40 Nm to 150 Nm perdegree of relative rotation of the flywheel masses.
 10. A twin massflywheel as defined in claim 7 in which the ratio of the combinedassister spring rate to the combined spring rate of the end stopresilient means is in the range 1:2 to 1:6.
 11. A twin mass flywheel asdefined in claim 7 in which the total travel of the end stop resilientmeans in the drive direction is less than 30% of the total travel of theassister springs.
 12. A twin mass flywheel as defined in of claim 7 inwhich each end stop resilient means is mounted between first abutmentson one flywheel mass and after a pre-determined amount of relativerotation in either of the drive and over-run directions second abutmentson the other flywheel mass act to compress each end stop resilient meansand thus cushion relative rotation of the flywheel masses.
 13. A twinmass flywheel as defined in claim 12 in which each assistor spring ismounted between third abutments on said one flywheel and a fourthabutment on the said other flywheel mass acts on one end of the assistorspring to compress the assistor spring.
 14. A twin mass flywheel asdefined in claim 13 in which the first abutments of an end stopresilient means and a third abutment of an associated assistor springare partially defined by a common support member.
 15. A twin massflywheel as defined in claim 14 in which the common support member alsoacts as part of the end stops to limit the relative rotation of theflywheel masses.
 16. A twin mass flywheel as defined in claim 13 inwhich each common support member supports and guides shoes at oppositeend of the associated end stop resilient means during compression of theend stop resilient means in either of the drive and over-run direction.17. A twin mass flywheel as defined in claim 7 in which each end stopresilient means consists of a pair of concentric springs acting inparallel.
 18. A twin mass flywheel as defined in claim 7 in which eachend stop resilient means comprises at least one members of elastomericmaterial.
 19. A twin mass flywheel as defined in claim 7 in which thecombined spring rate of the or all end stop resilient means issignificantly greater than the combined spring rate of the assistorsprings.
 20. A twin mass flywheel comprising two co-axially arrangedflywheel masses which are mounted for limited angular rotation in adrive and over-run direction relative to each other, and a plurality ofpivotal linkages comprising a first link pivotally connected to one ofthe flywheel masses a second link pivotally connected to the other ofthe flywheel masses and a pivot pivotally connecting the first andsecond links, in which the action of the links controls relativerotation of the flywheel masses, and the controlling action of the linksis supplemented by one or more assister springs and is furthersupplemented by one or more end stop springs.
 21. A twin mass flywheelcomprising two co-axially arranged flywheel masses which are mounted forlimited angular rotation in a drive and over-run direction relative toeach other, and a first resilient means which operates over asignificant proportion of full drive direction or over-run directionrange of relative rotation and a second resilient means which operatetowards the end of the full drive or over-run direction range ofrelative rotation in which a common support member partially supportsboth ends of the second resilient means and one end of the firstresilient means.
 22. A twin mass flywheel as defined in claim 21 whichincludes end stops to positively limit relative rotation of the flywheelmasses in the drive and over-run directions and the common supportmember acts as part of the end stops.